The present invention relates to electroplating and, more particularly, to the high speed, continuous electroplating of wire.
Typically the electroplating of wire involves applying a negative electrical charge to the wire so that it becomes a cathode and then passing the wire through an electrolyte bath that contains a positive electrode or anode. This anode creates positive metallic ions which are attracted to the wire and plate it. This process is often repeated by passing the wire through the bath several times or by passing it through other electrolyte baths arranged in series with the first.
After each such pass through a bath, the wire is brought out of the electrolyte and into contact with a negative electrode to reestablish the negative electrical charge that is needed to attract additional positive metal ions in the succeeding bath. This recharging of the wire cannot be done in the bath because the cathode itself would become plated with the positive metal ions. However this recharging is necessary because the positive metal ions that reach the wire have their charge neutralized as they are deposited on the wire. This neutralization of the ion charge creates a charge barrier to the accumulation of additional ions, which barrier is overcome by recharging the coated surface of the wire.
Various means have been proposed for charging wire prior to passing it through an electroplating bath. These include passing the wire over electrically charged rollers or through charged beds located outside the bath. See for example U.S. Pat. No. 3,947,343 to Delves-Broughton et al. As a result, the wire must be bent significantly a number of times as it passes back and forth through the bath or through subsequent baths. This bending requirement creates a limit on the gauge of the wire that can be used in such a process. Further heavy duty machines must be used to move the wire through these baths because of the resistance offered by the bends in the wire. Consequently, it is possible to stretch and break the wire unintentionally, especially in a high speed wire plating operation. It should also be noted that the longer the wire remains in the electroplating bath without being recharged, the less it is capable of attracting metal ions to its surface. Therefore, there is a limit to the length of the bath or the period of time in which the wire should be kept in the bath in order to assure efficient operation.